At the order level, the distribution of bacteria in the 12 soil samples of the proximal group (CR) was shown in Fig. 1.1. Among them, the number of common bacteria in 12 soil samples of the proximal group (CR) was 72, and the number of unique bacteria in the 12 soil samples was different. Among them, the number of unique bacteria in MSO1 soil samples was 5, only 1unique bacteria in MSO3 and CMSO23 soil samples, no unique bacteria in the other 9 soil samples. The bacterial distribution of 8 soil samples in the distal group (FBR) was shown in Figure.1.2. The number of common bacteria in the 8 soil samples of the distal group (FBR) was 56, of which 10 unique bacteria in the GMSO651 soil sample, 3 unique bacteria in the GMSO503 soil sample, 2 unique bacteria in the GMSO653 soil sample, and 1unique bacteria in the GMSO500 soil sample. The results of bacterial distribution of all 20 soil samples showed that the number of bacteria in each sample of 12 soil samples in the proximal group (CR) was about 72, and in each sample of 8 soil samples in the distal treatment group (FBR) was about 58. The number of bacteria in the high-mercury soil near the mercury mining area was higher than that in the medium-high-mercury soil far from the mercury mining area.
At the order level, the distribution of fungi in 12 soil samples of the proximal group (CR) was shown in Fig. 1.3. The total number of fungi in all 12 soil samples was 30, but the number of unique fungi to each of the 12 soil samples was different. Among them, the number of unique fungi in MSO3 soil samples was 3. 2 unique fungi in CMSO21, CMSO23, CMSO24, GMSO302, GMSO303 soil samples, 1unique fungi in MSO2 and MSO4 soil samples, and 0 unique fungi in MSO1, CMSO22, GMSO301, GMSO304 soil samples. The distribution of fungi in 8 soil samples of the distal group (FBR) was shown in Fig. 1.4. The number of common fungi in 8 soil samples was 19, of which 9 unique fungi in GMSO501 soil samples, 5 unique fungi in GMSO503 soil samples, 3 unique fungi in GMSO654 soil samples, 1 unique fungi in GMSO500 and GMSO651 soil samples, and 0 unique fungi in GMSO652 and GMSO653 soil samples. From the analysis of the number of fungi in all 20 soil samples, the number of fungi per sample in the 12 soil samples of the proximal group (CR) was about 31, and the number of fungi per soil sample in the 8 soil samples of the distal group (FBR) was about 22. The number of fungi in the high-mercury soil near the mercury mining area was higher than that in the medium-high-mercury soil far from the mercury mining area. At the order level, the total number of bacterial in both the proximal group and the distal group was higher than the total number of fungi.
At the family level, the bacterial distribution of 12 soil samples in the proximal group (CR) was shown in Fig. 1.5. The total number of bacteria in all 12 soil samples was 114, and the number of unique bacteria to each of the 12 soil samples was very different. Among them, the number of unique bacteria in MSO1 soil samples was 10. 1 unique bacteria in MSO2, MSO3, MSO4, CMSO21, CMSO22, CMSO23 and CMSO24 soil samples, while 0 unique bacteria in GMSO301, GMSO302, GMSO303 and GMSO304 soil samples. The distribution of bacteria in 8 soil samples of the distal group (FBR) was shown in Fig. 1.6.There were 89 bacteria in the 8 soil samples of the distal group (FBR), and the number of unique bacteria in 8 soil samples was quite different. Among them, the number of unique bacteria in GMSO651 soil samples was 22, 7 unique bacteria inGMSO653 soil samples, 3 unique bacteria in GMSO500, GMSO503 and GMSO652 soil samples, 1unique bacteria in GMSO502 soil samples, 0 unique bacteria in GMSO501 and GMSO654 soil samples. From the analysis of the number of bacteria in all 20 soil samples, the number of bacteria in each sample of the 12 soil samples in the proximal group (CR) was about 115, and the number of bacteria in each soil sample of the 8 soil samples in the distal group (FBR) was about 92. The number of bacteria in the high-mercury soil near the mercury mining area was higher than that in the medium-high-mercury soil far from the mercury mining area.
At the family level, the distribution of fungi in 12 soil samples of the proximal group (CR) was shown in Fig. 1.7. In the proximal group (CR), the number of common fungi in 12 soil samples was 36, and the number of unique fungi in 12 soil samples was very different. Among them, the number of unique fungi in CMSO21 soil samples was 7, 6 unique fungi in MSO4 and GMSO302 soil samples, 5unique fungi in MSO3 soil samples, 4 unique fungi in MSO2 and CMSO24 soil samples, 3 unique fungi in GMSO303, GMSO304, CMSO23 soil samples. 1unique fungi in CMSO22 and GMSO301 soil samples, while 0 unique fungi in MSO1 soil samples. The distribution of fungi in 8 soil samples of the distal group (FBR) was shown in Fig. 1.8. The number of common fungi in the 8 soil samples of the distal group (FBR) was 16, and the number of unique fungi among the soil samples was very different. Among them, the number of unique fungi in GMSO503, GMSO501 and GMSO502 soil samples was 22,19 and 15, respectively, while 1unique fungi in GMSO500 soil samples. Among GMSO651, GMSO652, GMSO653 and GMSO654 soil samples, only GMSO654 soil samples had 6, GMSO651 and GMSO653 soil samples had 1, and GMSO652 soil samples had 0. From the distribution of fungi in all 20 soil samples, the number of fungi in each sample of 12 soil samples in the proximal group (CR) was about 39, and the number of fungi in each sample of 8 soil samples in the distal group (FBR) was about 22.
Distribution of bacteria and fungi at Genus level at different distances from mercury mining area
At the genus level, the bacterial distribution of 12 soil samples in the proximal group (CR) was shown in Fig. 1.9. The number of common bacteria in the 12 soil samples in the proximal group (CR) was 173, and the number of unique bacteria to each of the 12 soil samples was very different. Among them, the number of unique bacteria to the MSO1 soil sample was the highest, reaching 29. 1,4, and 1unique bacteria in MSO2, MSO3, and MSO4 soil samples respectively. 3,5,3, and 2 unique bacteria in CMSO21, CMSO22, CMSO23, and CMSO24 soil samples respectively. 1,1,0,1unique bacteria in GMSO301, GMSO302, GMSO303 and GMSO304 soil samples respectively. The bacterial distribution of 8 soil samples in the distal (FBR) group was shown in Fig. 2.0. The number of common bacteria in 8 soil samples in the distal group (FBR) was 101, and the number of unique bacteria to each soil sample varies greatly. Among them, the number of unique bacteria in GMSO651 soil samples was 62, and 12,14,1 unique bacteria in the GMSO652, GMSO653, and GMSO654 soil samples respectively. 4,6,3 and 3 unique bacteria in GMSO500, GMSO501, GMSO502 and GMSO503 soil samples respectively. According to the bacterial distribution of all 20 soil samples, the number of bacterial distribution in each sample of 12 soil samples in the proximal group (CR) was about 177, while the number of bacterial distribution in each sample of 8 soil samples in the distal group (FBR) was about 114, the results indicated that the number of bacterial distribution in high mercury soil near the mercury mining area was much higher than that in medium-high mercury soil far away from the mercury mining area.
At the genus level, the distribution of fungi in 12 soil samples of the proximal group (CR) was shown in Fig. 2.1. The number of common fungi in the 12 soil samples of the proximal group (CR) was 21, but there was a big difference in the number of unique fungi among the 12 soil samples. The number of unique fungi in MSO1, MSO2, MSO3 and MSO4 soil samples was 2,13,14,21, respectively. 22,5,12,16 unique fungi in CMSO21, CMSO22, CMSO23 and CMSO24 soil samples respectively. 6,10,11,12 unique fungi in GMSO301, GMSO302, GMSO303 and GMSO304 soil samples respectively. The distribution of fungi in 8 soil samples of the distal group (FBR) was shown in Fig. 2.2. The total number of fungi in the 8 soil samples of the distal group (FBR) was 12, but the number of unique fungi among the 8 soil samples varies greatly. Among them, the number of unique fungi in GMSO500, GMSO501, GMSO502, GMSO503 was 8,50,44,55, respectively, and 14,6,2,11 unique fungi in GMSO651, GMSO652, GMSO653, GMSO654 soil samples respectively. From the distribution of fungi in all 20 soil samples, the number of fungi each sample in the 12 soil samples of the proximal group (CR) was about 33, and the number of fungi per sample in the 8 soil samples of the distal group (FBR) was about 35, the results indicated that the number of fungi in the high-mercury soil near the mercury mining area was close to the number of fungi in the low-mercury soil far from the mercury mining area. And at the genus level, the total number of bacterial in each soil sample in both the proximal group and the distal group was higher than the total number of fungi.
The relative abundance of soil bacteria and fungi at the order level at different distances from mercury mining areas
At the order level, the relative abundance of bacteria in 20 soil samples was shown in Fig. 2.3.The bacteria with higher average relative abundance in MSO1, MSO2, MSO3 and MSO4 high mercury soil samples were Sphingomonadales(8.74%),Rhizobiales(8.38%), Sphingobacteriales (7.78%), Gp4 (norank_Acidobacteria_Gp4) (5.16%), Flavobacteriales(4.28%), Gp6(norank_Acidobacteria_Gp6)(4.14%), Burkholderiales(3.94%), Pseudomonadales (3.68%), Xanthomonadales (3.05%), Rhodospirillales (3.04%). The bacteria with higher average relative abundance in CMSO21, CMSO22, CMSO23 and CMSO24 were Sphingobacteriales(9.10%), Gp6(norank_Acidobacteria_Gp6)(5.14%), Sphingomonadales(4.96%),Anaerolineales(4.83%),Rhodospirillales(3.85%),Planctomycetales(3.77%), Rhizobiales (3.53%), Flavobacteriales (3.45%), Xanthomonadales (2.93%), Gp4(norank_Acidobacteria_Gp4)(2.78%). The bacteria with higher average relative abundance in CMSO301, CMSO302, CMSO303 and CMSO304 were Sphingomonadales(8.88%), Gp4(norank_Acidobacteria_Gp4)(8.83%),Sphingobacteriales(7.33%),Gp6(norank_Acidobacteria_Gp6)(7.12%),Rhodospirillales(4.38%),norank_Spartobacteria(4.10%),Planctomycetales(4.06%),Rhizobiales(3.82%),Xanthomonadales(3.52%),Actinomycetales(2.88%). The bacteria with higher average relative abundance in GMSO500, GMSO501, GMSO502 and GMSO503 were Sphingomonadales(11.31%), Sphingobacteriales(9.97%), Gp4(norank_Acidobacteria_Gp4)(6.90%), Gp6(norank_Acidobacteria_Gp6)(5.32%),Rhizobiales(4.30%),Anaerolineales(4.23%),Gemmatimonadales(4.21%),Rhodospirillales(3.35%),Planctomycetales(2.67%),Gp3(norank_Acidobacteria_Gp3)(2.67%),Actinomycetales(2.64%),Burkholderiales (2.50%). The bacteria with higher average relative abundance in GMSO651, GMSO652, GMSO653 and GMSO654 were Burkholderiales(20.01%),Bacteroidales(10.27%),Sphingomonadales(7.24%),Sphingobacteriales(4.60%), Gp1(norank_Acidobacteria_Gp1)(4.47%),Caulobacterales(4.39%),Rhizobiales(3.79%),Clostridiales (3.43%), Gp3( norank_ Acidobacteria_Gp3) (2.89%).
At the order level, the relative abundance of fungi in 20 soil samples was shown in Fig. 2.4. The fungi with higher average relative abundance in MSO1, MSO2, MSO3, and MSO4 were Agaricales(63.48%), Sebacinales(8.36%), Hypocreales(5.59%), Archaeorhizomycetales(2.98%), Chaetothyriales(2.67%), Capnodiales (2.59%), Mortierellales(2.10%), Helotiales(2.04%). The fungi with higher average relative abundance in CMSO21, CMSO22, CMSO23 and CMSO24 were Sebacinales(28.34%), Mortierellales(19.24%), Trechisporales(6.94%), Helotiales(2.77%),Hypocreales(2.70%), Pleosporales (2.67%), Lulworthiales(2.31%),Orbiliales(2.31%), Auriculariales(2.03%).The fungi with higher average relative abundance in CMSO301, CMSO302, CMSO303 and CMSO304 were Agaricales(65.13%), Archaeorhizomycetales(15.27%), Sebacinales(5.74%) and Chaetothyriales(2.13%). The fungi with higher average relative abundance in GMSO500, GMSO501, GMSO502, and GMSO503 were Agaricales(23.93%), Geoglossales(14.46%), Sebacinales(12.62%), Archaeorhizomycetales(7.42%),Corticiales(6.99%), Sordariales(4.04%), Pleosporales(3.21%),Chaetothyriales(2.911%), Onygenales(2.81%), Mortierellales(2.41%), Pezizales(2.25%), Russulales(2.16%).The fungi with higher average relative abundance in GMSO651, GMSO652, GMSO653 and GMSO654 were Helotiales(16.03%), Mortierellales(8.88%), Sebacinales (8.17%), Saccharomycetales (6.06%) ,Sordariales (5.54%). Hypocreales (4.85%), Chaetothyriales (4.64%), Pleosporales (4.38% ), Geoglossales (4.03%), Russulales (3.80%), Polyporales (3.65%), Archaeorhizomycetales (3.14%). Capnodiales (2.61%), Tremellales (2.50%), Agaricales (2.32%).
The relative abundance of bacteria and fungi at the family level at different distances from the mercury mining area.
At the family level, the relative abundance of bacteria in each soil sample was shown in Fig. 2.5. The bacteria with higher average relative abundance in MSO1,MSO2,MSO3,and MSO4 were Sphingomonadaceae(8.01%), Chitinophagaceae(6.57%),Gp4(norank_Acidobacteria_Gp4)(5.16%),Flavobacteriaceae(4.22%),Gp6(norank_ Acidobacteria_Gp6)(4.14%),Pseudomonadaceae(2.89%),Planctomycetaceae(2.85%),Enterobacteriaceae(2.63%), Xanthomonadaceae (2.12%), Comamonadaceae (2.02%). The bacteria with higher average relative abundance in CMSO21, CMSO22, CMSO23 and CMSO24 were Chitinophagaceae(7.71%), Gp6(norank_Acidobacteria_Gp6)(5.14%), Anaerolineaceae(4.83%), Sphingomonadaceae(4.74%),Planctomycetaceae(3.77%), Flavobacteriaceae(3.43%), Gp4 (norank_Acidobacteria_Gp4) (2.78%), Rhodospirillaceae(2.15%), Gemmatimonadaceae (2.12%).The bacteria with higher average relative abundance in CMSO301, CMSO302, CMSO303 and CMSO304 were Gp4 (norank_Acidobacteria_Gp4) (8.83%), Sphingomonadaceae (8.43%), Gp6 (norank_Acidobacteria_Gp6)(7.12%), Chitinophagaceae(6.97%), Norank _Spartobacteria(4.10%), Planctomycetaceae(4.06%), Rhodospirillaceae(3.04%). The bacteria with higher average relative abundance in GMSO500, GMSO501, GMSO502 and GMSO503 were Sphingomonadaceae(10.93%), Chitinophagaceae (9.42%) and Gp4(norank_Acidobacteria_Gp4)(6.90%), Gp6(norank_Acidobacteria_Gp6)(5.32%),Anaerolineaceae (4.23%), Gemmatimonadaceae (4.21%), Planctomycetaceae (2.67%), Gp3 (norank_Acidobacteria_Gp3) (2.66%). The bacteria with average relative abundance in GMSO651, GMSO652, GMSO653 and GMSO654 were Burkholderiaceae(13.81%), Porphyromonadaceae(8.40%), Sphingomonadaceae(7.16%),Oxalobacteraceae (4.75%), Gp1 (norank_ Acidobacteria_Gp1 ) (4.47%),Caulobacterales(4.37%),Chitinophagaceae(4.26%),Gp3(norank_Acidobacteria_Gp3)(2.89%), Gemmatimonadaceae (2.16%).
At the family level, the relative abundance of bacteria in each soil sample was shown in Fig. 2.5. The bacteria with higher average relative abundance in MSO1, MSO2, MSO3, and MSO4 were Sphingomonadaceae(8.01%), Chitinophagaceae(6.57%),Gp4(norank_Acidobacteria_Gp4)(5.16%),Flavobacteriaceae(4.22%),Gp6(norank_ Acidobacteria_Gp6)(4.14%),Pseudomonadaceae(2.89%),Planctomycetaceae(2.85%),Enterobacteriaceae(2.63%), Xanthomonadaceae (2.12%). Comamonadaceae (2.02%).The bacteria with higher average relative abundance in CMSO21, CMSO22, CMSO23 and CMSO24 were Chitinophagaceae(7.71%), Gp6(norank_Acidobacteria_Gp6)(5.14%), Anaerolineaceae(4.83%),Sphingomonadaceae(4.74%),Planctomycetaceae(3.77%),Flavobacteriaceae(3.43%),Gp4 (norank_Acidobacteria_Gp4) (2.78%), Rhodospirillaceae (2.15%), Gemmatimonadaceae (2.12%). The bacteria with higher average relative abundance in CMSO301, CMSO302, CMSO303 and CMSO304 were Gp4 (norank_ Acidobacteria_Gp4 ) (8.83%),Sphingomonadaceae(8.43%),Gp6(norank_Acidobacteria_Gp6)(7.12%),Chitinophagaceae (6.97%),Norank_Spartobacteria(4.10%),Planctomycetaceae(4.06%), Rhodospirillaceae(3.04%).The bacteria with higher relative abundance in GMSO500,GMSO501,GMSO502 and GMSO503 were Sphingomonadaceae(10.93%), Chitinophagaceae(9.42%),Gp4(norank_Acidobacteria_Gp4)(6.90%),Gp6(norank_Acidobacteria_Gp6)(5.32%), Anaerolineaceae(4.23%),Gemmatimonadaceae(4.21%),Planctomycetaceae(2.67%),Gp3(norank_Acidobacteria_Gp3)(2.66%). The bacteria with higher average relative abundance in GMSO651, GMSO652, GMSO653 and GMSO654 were Burkholderiaceae(13.81%),Porphyromonadaceae(8.40%),Sphingomonadaceae(7.16%),Oxalobacteraceae(4.75%),Gp1(norank_Acidobacteria_Gp1)(4.47%),Caulobacterales(4.37%),Chitinophagaceae(4.26%),Gp3(norank_Acidobacteria_Gp3)(2.89%),Gemmatimonadaceae (2.16%).
At the family level, the relative abundance of fungi in 20 soil samples was shown in Fig. 2.6. The fungi with higher average relative abundance in MSO1, MSO2, MSO3, and MSO4 were Hygrophoraceae (58.45%), Clavariaceae (4.03%), Nectriaceae (3.08%), Archaeorhizomycetace (2.98%). Herpotrichiellaceae (2.26%), Mortierellaceae (2.09%), Helotiaceae (1.91%), Sebacinaceae (1.82%). The fungi with higher average relative abundance in CMSO21, CMSO22, CMSO23 and CMSO24 were Sebacinaceae (28.02%), Mortierellaceae (19.24%), Hygrophoraceae (6.94%), Nectriaceae (1.22%), Cucurbitariaceae (1.21%). Hyaloscyphaceae (1.09%).The fungi with higher average relative abundance in CMSO301, CMSO302, CMSO303 and CMSO304 were Hygrophoraceae(26.34%), Tricholomataceae(21.18%), Clavariaceae(17.10%),Archaeorhizomycetace(15.27%),Serendipitaceae (4.85%), Herpotrichiellaceae (1.98%), Nectriaceae (1.28%), Mortierellaceae(1.18%). The fungi with higher average relative abundance in GMSO500, GMSO501, GMSO502 and GMSO503 were Geoglossaceae(14.37%), Clavariaceae(12.94%), Archaeorhizomycetace(7.42%),Corticiaceae (6.99%). Serendipitaceae (6.30%), Sebacinaceae (5.58%), Entolomataceae (5.14%), Hygrophoraceae (4.55%), Lasiosphaeriaceae (3.09%), Mortierellaceae (2.41%), Pyronemataceae (2.23%), Russulaceae (2.14%).The fungi with higher average relative abundance in GMSO651, GMSO652, GMSO653 and GMSO654 were Helotiaceae (10.16%), Mortierellaceae (8.88%), Sebacinaceae (6.17%), Nectriaceae (4.15%), Geoglossaceae (4.03%). Lasiosphaeriaceae (3.85%), Russulaceae (3.80%), Saccharomycetaceae (3.48%), Archaeorhizomycetace (3.14%), Mycosphaerellaceae (2.52%), Podoscyphaceae (2.51%). Trichocomaceae (2.20%).
The relative abundance of bacteria and fungi at the genus level in soils at different distances from mercury mining areas.
At the genus level, the relative abundance of bacteria in 20 soil samples was shown in Fig. 2.7. The bacteria with higher average relative abundance in MSO1, MSO2, MSO3, and MSO4 were Gp6 (norank_Acidobacteria_Gp6) (4.14%), Flavobacterium(4.12%),Sphingomonas(3.77%),Gp4(norank_Acidobacteria_Gp4)(3.49%),Pseudomonas(2.72%),Buttiauxella(2.44%),Saccharibacteria_genera_incertae_sedis(1.77%),Gp3(norank_Acidobacteria_Gp3)(1.42%),Lacibacterium (1.34%),Terrimonas (1.28%), Rhizobium (1.15% ), Gp7 (1.08%), Gemmatimonas (1.06%). The bacteria with higher average relative abundance in CMSO21, CMSO22, CMSO23 and CMSO24 were Acidobacteria Gp6(5.14%), Flavobacterium (3.37%), Sphingomonas (3.30%), Gemmatimonas (3.19%), Lacibacterium (2.12%), Gp4 (1.78%), Gp3 (1.71%), Subdivision3_genera_incertae_sedis (1.55%), Geobacter (1.20%), Lysobacter (1.03%). The bacteria with higher average relative abundance in CMSO301, CMSO302, CMSO303 and CMSO304 were Gp4(7.20%), Gp6(7.12%), Sphingomonas(4.11%),Spartobacteria_genera_incertae_sedis(3.82%),Lacibacterium(2.88%),Subdivision3_genera_incertae _ sedis (2.49%), WPS-1_genera_incertae_sedis (2.13%), Terrimona(1.43%), Lysobacter (1.36%), Gp3(1.32%), Gaiella (1.15%), Pirellula (1.05%). The bacteria with higher average relative abundance in GMSO500, GMSO501, GMSO502 and GMSO503 were Gp6 (5.32%), Sphingomonas (4.70%), Gp4 (4.40%), Gemmatimonas (4.21% ), Gp3 (2.37%) and Streptophyta(2.24%),Spartobacteria_genera_incertae_sedis(1.84%),Lacibacterium(1.69%),WPS-1_genera_incertae_sedis(1.69%), Pseudomonas (1.60%), Subdivision3_genera_incertae_sedis (1.30%), Gp7 (1.10%).The bacteria with higher average relative abundance of GMSO651, GMSO652, GMSO653 and GMSO654 were Ralstonia (13.49%), Herbaspirillum (4.43%), Phenylobacterium (4.33%), Gp1 (2.92%), Gp3 (2.54%) and Gemmatimonas(2.16%). Gp2 (1.80%), Lactobacillus (1.80%), Sphingomonas (1.64% ), Acinetobacter(1.33%), Spartobacteria_genera_incertae_sedis (1.30%), Gp6 (1.04%).
At the genus level, the relative abundance of fungi in each soil sample was shown in Fig. 2.8. The fungi with higher average relative abundance in MSO1, MSO2, MSO3, and MSO4 were Hygrocybe(58.45%), Clavaria(4.03%), Archaeorhizomyces(2.98%), Fusarium(2.88%), Mortierella(2.09%), Brachysporium(1.73%), Exophiala(1.57%), Neodevriesia (1.43%), Serendipita (1.26%), Tetracladium (1.06%).The fungi with higher average relative abundance in CMSO21, CMSO22, CMSO23 and CMSO24 were Helvellosebacina (27.85%), Mortierella (19.24%), Trechispora (6.94%), Oliveonia (1.90%), Pyrenochaetopsis(1.14%).The fungi with higher average relative abundance in CMSO301, CMSO302, CMSO303 and CMSO304 were Hygrocybe (26.34%), Dermoloma(21.04%), Clavaria(17.10%), Archaeorhizomyces (15.27%), Serendipita (4.85%), Mortierella(1.13% ). The fungi with higher average relative abundance in GMSO500, GMSO501, GMSO502 and GMSO503 were Trichoglossum(13.9%), Clavaria(12.94%), Archaeorhizomyces(7.42%), Serendipita(6.30%), Entoloma(5.06%), Hygrocybe(4.55%), Sebacina(3.76%), Mortierella(2.07%), Cercophora(1.84%), Knufia (1.37%), Russula (1.78%).The fungi with higher average relative abundances in GMSO651, GMSO652, GMSO653 and GMSO654 were Collophora(9.74%), Mortierella(8.88% ), Sebacina(3.84%), Archaeorhizomyces(3.14%),Kazachstania (2.97%), Trichoglossum (2.73%), Cotylidia (2.51%), Lactifluus (2.29%), Echria (2.21%), Knufia (2.10%), Sphaerulina (1.78%), Serendipita (1.63%), Ilyonectria (1.54%), Russula (1.51%).
Discussion and conclusions
Mercury is one of the most common heavy metal pollutants in the environment. Soil mercury pollution is often closely related to the mining of surrounding mercury-related metal mines and the smelting of mercury-related metals. Once soil is polluted by mercury, it will be transferred to plant roots, stems, leaves and other parts through plant enrichment. When the soil mercury content reaches a certain level, it will seriously affect the normal growth and development of plants, and will further transfer to other animals through the enrichment of the food chain, which will cause great damage to animal nerve function20,21. On the other hand, when the soil is polluted by heavy metals, it will have adverse effects on the soil ecosystem, especially on soil microorganisms and soil animals22. Previous studies have confirmed that the concentration of Cd, Zn, Pb and Cu in soil has a strong correlation with soil microbial biomass23, and different microbial groups have different tolerance to different heavy metals24. The reason why heavy metals have adverse effects on microbial diversity may be that high concentrations of heavy metals have a certain restrictive effect on microbial cell metabolism and other functions, which ultimately leads to a decrease in microbial diversity25.
In this work, the results of bacterial and fungal diversity in soils with different mercury contents at different distances from mercury mining areas showed that the number of bacteria and fungi in 20 soil samples at different distances from mercury mining areas increased significantly according to the order of order, family and genus, and the increase of bacterial number was much higher than that of fungal number, especially at the family level and genus level. The number of bacteria and fungi unique to each of the 20 soil samples showed a significant increase trend. This result showed that even in a certain mercury stress environment, the number of bacteria and fungi in the soil around the mercury mining area increases with the decrease of the classification level, which was not affected by soil mercury and other factors. In this study, there were some differences in the number of unique bacteria and fungi to the four repeated soil samples at different points in the same distance from the mercury mining area, and even the number of unique bacteria and fungi to individual samples in the four repeated soil samples of the same group was abnormal. These results indicated that in the outdoor natural environment, the diversity distribution of bacteria and fungi in the soil at different points in the same range was not affected by the internal factors of the soil. For example, when the mercury content in the soil at different points in the same range was basically close, the diversity of bacteria and fungi was affected by many factors, resulting in the difference in the number of bacteria and fungi unique to individual soil samples26. It also showed that there was a certain heterogeneity in the soil around the mercury mining area. Therefore, it can be speculated that heavy metal mercury pollution will lead to a decline in soil microbial diversity to a certain extent, but the relationship between the two was not a simple linear relationship, but also affected by other factors within the soil.
The results of this study showed that the number of bacteria in 2–20 m high mercury soil samples from mercury mining area was much higher than that in 30–650 m medium-high mercury soil samples from mercury mining area at any classification level of order, family and genus. The distribution of the number of fungi was very similar to the distribution of the number of bacteria, that is, the number of bacteria and fungi in the soil with high mercury concentration was higher than that in the soil with high mercury concentration at any level of order, family and genus. This result was inconsistent with the research results of Shan et al.27 and Li et al.9. The main reason was that the soil mercury concentration was very different. The soil mercury concentration range in this work is 45.42-175.02 mg/kg. The second reason was that the experimental environment was different. Previous studies belong to the soil environment of artificial simulation laboratory. This study was the natural soil environment of mercury mining area, various bacteria in soil samples, and fungi reach an equilibrium state after a long period of comprehensive influence of various factors inside the soil. From the perspective of resistance to heavy metal mercury, the real existence of these bacteria and fungi was a good adaptation to the soil 's own environment, indicating that these bacteria and fungi were highly adapted to the mercury stress environment for a long time. The reason for this result may be related to the different types of soil. Maliszewska et al.28found that the compounds of Cu and Hg showed the strongest inhibitory effect on microbial proliferation, and the order of toxicity of HgCl2 to microorganisms was bacteria > fungi > actinomycetes. The results showed that the inhibitory effect of mercury on microbial proliferation was fluctuating, and the inhibition of microorganisms decreased with the prolongation of culture time27.In this study, the soil around the mercury mining area has been subjected to high concentration mercury pollution stress for a long time. The increase in the number of bacteria and fungi under high concentration mercury environment may be the best evidence that the inhibition of bacteria and fungi decreases with time.
The community structure of bacteria, fungi and actinomycetes in soil is easily affected by environmental variables around the soil, such as nutrient cycling and heavy metal concentration changes29,30. In this work, the effects of mercury concentration on the community structure of bacteria and fungi at the order, family and genus levels were analyzed. It was found that mercury had a certain effect on the community structure of bacteria and fungi, and the tolerance of different bacteria and fungi to mercury pollution was also very different, which was consistent with the results of Prasad31.In terms of changes in bacterial community structure, at the level of order, family and genus, the bacteria with high relative abundance in both high mercury (119.51-175.02 mg/kg ) soil and medium high mercury (45.42–72.31 mg/kg ) soil changed. At the order level, the bacteria with high relative abundance were Sphingomonadales and Sphingobacteriales. The relative abundance remained at about 10%, which was the dominant bacteria in the soil. This fully demonstrated that Sphingomonadales and Sphingobacteriales were very resistant to mercury pollution. At the family level, the bacteria with high relative abundance were Sphingomonadaceae and Chitinophagaceae, which were the dominant bacteria in the soil. The bacteria with high relative abundance at the genus level were Gp6(norank_Acidobacteria_Gp6),Sphingomonas,Gp4 (norank_Acidobacteria_Gp4).Similarly, in terms of the effect of different concentrations of mercury on the fungal community structure, at the order level, the fungi with the highest relative abundance in both high-mercury soil and medium-high mercury soil were Agaricales and Sebacinales. At the level of family, the fungi with the highest relative abundance in both high-mercury soil and medium-high mercury soil were Sebacinaceae and Hygrophoraceae. At the genus level, Hygrocybe and Sebacina had the highest relative abundance, which were the dominant fungi in soil and showed strong mercury tolerance. Regardless of the classification level, bacteria and fungi with high relative abundance as the dominant bacteria in the soil were the performance of long-term adaptation to high mercury and medium-high mercury soil environment, indicating that these bacteria have strong tolerance to high concentration mercury stress. This was similar to the conclusion of Feris32 and Gillan et al33. At the same time, at any level of order, family and genus, the types of bacteria and fungi with high relative abundance in different positions of mercury mining area were quite different, which was closely related to the heterogeneity of many factors in the internal environment of soil 22.
There is a complex mutual utilization relationship between plants and rhizosphere microorganisms. Microorganisms can usually affect the photosynthesis, physiological and biochemical metabolic processes of plants, and then have adverse effects on plant growth and root function. Therefore, it was of great significance to study the synergistic survival relationship between rhizosphere microorganisms and plants under heavy metal stress, make full use of soil microorganisms to effectively protect plants from heavy metal stress, and improve the survival of plants in heavy metal stress environment. Fully exploring the correlation between rhizosphere soil flora and plant growth provides an effective scientific reference for further exploring the mechanism of synergistic mercury enrichment between rhizosphere microorganisms and plants.